Active Antenna Arrays (AAA), otherwise known as smart antennas, have recently gained popularity as candidate technology for base stations (BS) of future cellular/mobile networks. In the context of AAA, each radiator of the BS antenna array is fed by a dedicated RF transceiver /RF front-end, as shown in FIG. 1. In FIG. 1, a base station 2 has an active antenna array comprising a series of N antenna elements 41 . . . 4N, each being coupled to a respective RF transceiver 61 . . . 6N. Typically each RF transceiver comprises a transmit path which includes a digital to analog converter DAC, a frequency up-conversion stage and a power amplifier PA, and a receive path which includes a low noise amplifier, a frequency down-conversion stage and an analog to digital converter ADC. Appropriate phase shifts are applied, either in the transceivers, or in baseband signal processing, to the transmit and receive paths of the array in order to “steer” the antenna beam.
Current and future base stations may be required to support different mobile telecommunication systems, e.g. 2G (e.g. GSM), 3G (e.g. WCDMA) or 4G (e.g. LTE), operating on different frequencies, which may be in a range from 400 MHz to 2.6 GHz. This might require separate antenna array configurations for each system, which is clearly costly and generally inconvenient